Influence of Specimen Geometries on the Compressive Strength of Lightweight Aggregate Concrete

Dept. of Architectural Engineering, Kyonggi University, Suwon 443-760, KoreaABSTRACT The current study prepared 9 laboratorial concrete mixes and 3 ready-mixed concrete batches to examine the sizeand shape effects in compression failure of lightweight aggregate concrete (LWC). The concrete mixes were classified into threegroups: normal-weight, all-lightweight and sand-lightweight concrete groups. For each concrete mix, the aspect ratio of circularor square specimens was 1.0 and 2.0. The lateral dimension of specimens varied between 50 and 150 mm for each laboratorial con-crete mix, whereas it ranged from 50 to 400 mm with an incremental variation of 50 mm for each ready-mixed concrete batch. Testobservations revealed that the crack propagation and width of the localized failure zone developed in lightweight concrete spec-imens were considerably different than those of normal-weight concrete (NWC). In LWC specimens, the cracks mainly passedthrough the coarse aggregate particles and the crack distribution performance was very poor. As a result, a stronger size effect wasdeveloped in LWC than in NWC. Especially, this trend was more notable in specimens with aspect ratio of 2.0 than in specimenswith that of 1.0. The prediction model derived by Kim et al. overestimated the size effect of LWC when lateral dimension of spec-imen is above 150 mm. On the other hand, the modification factors specified in ASTM and CEB-FIP provisions, which are usedto compensate for the shape effect of specimen on compressive strength, were still conservative in LWC.Keywords : size effect, compressive strength, lightweight aggregate concrete, shape of specimen